The perception of visual surfaces is central to the processes by which humans come to understand and control their environment. Tasks such as object recognition, grasping, and manipulation, and path planning and obstacle avoidance require reliable information about surface layout. The aim of this proposal is to study the assumptions used by human vision in its perception of visual surfaces. Particular attention will be focused on the assumption of "generic viewing position": Human vision assumes that the qualitative structure of an image is stable under small changes of viewpoint. The experiments will explore visual surface perception in a range of contexts, including, monocular line- drawings of surfaces, untextured stereo surfaces, and subjective surfaces (such as the Kanizsa triangle). The goal is to clearly delineate the empirical content, scope, and limits of the generic view principle, and to further scientific knowledge about the role of surface organization in 3-D perception.